Epigenetic age acceleration mediates the association between smoking and diabetes-related outcomes

Background Smoking can lead to the deterioration of lung function and susceptibility to diabetes. Recently, smoking was found to induce DNA methylation (DNAm) changes in some cytosine-phosphate-guanine sites (CpGs). As linear combinations of DNAm levels of aging-related CpGs, five measures of epigenetic age acceleration (EAA) have received extensive attention: HannumEAA, IEAA, PhenoEAA, GrimEAA, and DunedinPACE. It is of interest to explore whether some measures of EAA can mediate the associations of smoking with diabetes-related outcomes and indices of ventilatory lung function. Methods and results In this study, we included self-reported smoking variables (smoking status, the number of pack-years, and years since smoking cessation), seven DNAm markers (HannumEAA, IEAA, PhenoEAA, GrimEAA, DNAm-based smoking pack-years, DNAm plasminogen activator inhibitor 1 [PAI-1] levels, and DunedinPACE), and four health outcomes (fasting glucose, hemoglobin A1C, forced expiratory volume in 1.0 s [FEV1], and forced vital capacity [FVC]) from 2474 Taiwan Biobank participants. Mediation analyses were conducted while adjusting for chronological age, sex, body mass index, drinking status, regular exercise status, educational attainment, and five cell-type proportions. We demonstrated that GrimEAA, DNAm-based smoking pack-years, DNAm PAI-1 levels, DunedinPACE, and PhenoEAA mediated smoking associations with diabetes-related outcomes. Moreover, current and former smoking both had an adverse indirect effect on FVC through DNAm PAI-1 levels. For former smokers, a long time since smoking cessation had a positive indirect impact on FVC through GrimEAA and on FEV1 through PhenoEAA. Conclusions This is one of the first studies to comprehensively investigate the role of five measures of EAA in mediating the associations of smoking with the health outcomes of an Asian population. The results showed that the second-generation epigenetic clocks (GrimEAA, DunedinPACE, and PhenoEAA) significantly mediated the associations between smoking and diabetes-related outcomes. In contrast, the first-generation epigenetic clocks (HannumEAA and IEAA) did not significantly mediate any associations of smoking variables with the four health outcomes. Cigarette smoking can, directly and indirectly, deteriorate human health through DNAm changes in aging-related CpG sites. Supplementary Information The online version contains supplementary material available at 10.1186/s13148-023-01512-x.


Supplemental
(Based on 173,807 Taiwan Biobank participants) Results of regressing health outcomes on smoking variables while adjusting for six covariates (chronological age (in years), sex (male vs. female), BMI (in kg/m 2 ), drinking status (yes vs. no), performing regular exercise (yes vs. no), and educational attainment (an integer ranging from 1 to 7)) TABLE S3 (Only in males) Basic characteristics of the 1,243 male participants stratified by smoking status

FIGURE S4
(Only in males) 95% confidence intervals of the effects of six DNAm markers in mediating the associations between former smoking status and four health outcomes.

FIGURE S5
(Only in males) 95% confidence intervals of the effects of six DNAm markers in mediating the associations between current smoking status and four health outcomes.

FIGURE S6
(Only in males) 95% confidence intervals of the effects of six DNAm markers in mediating the associations between former smokers' pack-years and four health outcomes.

FIGURE S7
(Only in males) 95% confidence intervals of the effects of six DNAm markers in mediating the associations between current smokers' pack-years and four health outcomes. FIGURE S8 (Only in males) 95% confidence intervals of the effects of six DNAm markers in mediating the associations between years since smoking cessation and four health outcomes.  Tables   TABLE S1 Basic characteristics of the 173,807 Taiwan Biobank (TWB) participants  The characteristics are presented in n (%) or mean ± standard deviation.
a Former smokers were defined as those who "had previously smoked cigarettes for at least six months but had quit smoking for at least six months when participating in TWB." b Current smokers were defined as those who "had smoked cigarettes for at least six months and had not quit smoking when participating in TWB." c The p-value of testing the mean or proportion difference among non-smokers, former smokers, and current smokers was based on a Kruskal-Wallis test for continuous variables or a Chi-square test for sex, drinking, and regular exercise.
d Drinking was defined as those who "had a weekly intake of more than 150 mL of alcoholic beverages for at least six months and had not stopped drinking when participating in TWB".
e Regular exercise was defined as "performing exercise for 30 minutes thrice a week". 'Exercise' included leisure-time activities such as jogging, swimming, cycling, yoga, resistance training, hiking, etc.
f Educational attainment was an integer ranging from 1 to 7: 1 "illiterate", 2 "no formal education but literate", 3 "primary school graduate", 4 "junior high school graduate", 5 "senior high school graduate", 6 "college graduate", and 7 "Master's or higher degree".   and educational attainment (an integer ranging from 1 to 7)) Significant results with p < 0.05 are highlighted in bold font. FG and HbA1c were natural-log transformed and then standardized as z-scores; FEV1 and FVC were standardized as z-scores.
The characteristics are presented in n (%) or mean ± standard deviation.
a Former smokers were defined as those who "had previously smoked cigarettes for at least six months but had quit smoking for at least six months when participating in TWB." b Current smokers were defined as those who "had smoked cigarettes for at least six months and had not quit smoking when participating in TWB." c The p-value of testing the mean or proportion difference among non-smokers, former smokers, and current smokers was based on a Kruskal-Wallis test for continuous variables or a Chi-square test for sex, drinking, and regular exercise.
d Drinking was defined as those who "had a weekly intake of more than 150 mL of alcoholic beverages for at least six months and had not stopped drinking when participating in TWB".
e Regular exercise was defined as "performing exercise for 30 minutes thrice a week". 'Exercise' included leisure-time activities such as jogging, swimming, cycling, yoga, resistance training, hiking, etc.